Methods and systems for multi user uplink compatibility with legacy devices

ABSTRACT

Methods and apparatus for multiple user uplink are provided. In one aspect, a method of transmitting a physical layer convergence protocol data unit on a wireless medium includes generating a first portion and a second portion of the physical layer convergence protocol data unit, transmitting the first portion at a first data rate, the first portion decodable by a first and second sets of devices, and transmitting the second portion at a second data rate higher than the first data rate, the second portion decodable by the second set of devices.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/795,833, filed Jul. 9, 2015, and entitled “METHODS AND SYSTEMS FORMULTI USER UPLINK COMPATIBILITY WITH LEGACY DEVICES,” which claimspriority under 35 U.S.C. § 119(e) to U.S. Provisional Application No.62/023,740, filed Jul. 11, 2014, and entitled “METHODS AND SYSTEMS FORMULTI USER UPLINK COMPATIBILITY WITH LEGACY DEVICES,” and to U.S.Provisional Application No. 62/025,239, filed Jul. 16, 2014, andentitled “METHODS AND SYSTEMS FOR MULTI USER UPLINK COMPATIBILITY WITHLEGACY DEVICES,” and to U.S. Provisional Application No. 62/025,945,filed Jul. 17, 2014, and entitled “METHODS AND SYSTEMS FOR MULTI USERUPLINK COMPATIBILITY WITH LEGACY DEVICES.” The disclosures of each ofthese prior applications are considered part of this application, andare hereby each incorporated by reference herein in its entirety.

FIELD

Certain aspects of the present disclosure generally relate to wirelesscommunications, and more particularly, to methods and apparatus formultiple user uplink communication in a wireless network.

BACKGROUND

In many telecommunication systems, communications networks are used toexchange messages among several interacting spatially-separated devices.Networks may be classified according to geographic scope, which couldbe, for example, a metropolitan area, a local area, or a personal area.Such networks may be designated respectively as a wide area network(WAN), metropolitan area network (MAN), local area network (LAN), orpersonal area network (PAN). Networks also differ according to theswitching/routing technique used to interconnect the various networknodes and devices (e.g., circuit switching vs. packet switching), thetype of physical media employed for transmission (e.g., wired vs.wireless), and the set of communication protocols used (e.g., Internetprotocol suite, SONET (Synchronous Optical Networking), Ethernet, etc.).

Wireless networks are often preferred when the network elements aremobile and thus have dynamic connectivity needs, or if the networkarchitecture is formed in an ad hoc, rather than fixed, topology.Wireless networks employ intangible physical media in an unguidedpropagation mode using electromagnetic waves in the radio, microwave,infra-red, optical, etc. frequency bands. Wireless networksadvantageously facilitate user mobility and rapid field deployment whencompared to fixed wired networks.

In order to address the issue of increasing bandwidth requirements thatare demanded for wireless communications systems, different schemes arebeing developed to allow multiple user terminals to communicate with asingle access point by sharing the channel resources while achievinghigh data throughputs. With limited communication resources, it isdesirable to reduce the amount of traffic passing between the accesspoint and the multiple terminals. For example, when multiple terminalssend uplink communications to the access point, it is desirable tominimize the amount of traffic to complete the uplink of alltransmissions. Thus, there is a need for an improved protocol for uplinktransmissions from multiple terminals.

SUMMARY

Various implementations of systems, methods and devices within the scopeof the appended claims each have several aspects, no single one of whichis solely responsible for the desirable attributes described herein.Without limiting the scope of the appended claims, some prominentfeatures are described herein.

Details of one or more implementations of the subject matter describedin this specification are set forth in the accompanying drawings and thedescription below. Other features, aspects, and advantages will becomeapparent from the description, the drawings, and the claims. Note thatthe relative dimensions of the following figures may not be drawn toscale.

One aspect disclosed is a method of transmitting a physical layerconvergence protocol data unit on a wireless medium. The method includesgenerating a first portion and a second portion of the physical layerconvergence protocol data unit, transmitting the first portion at afirst data rate, the first portion decodable by a first and second setsof devices; and transmitting the second portion at a second data ratehigher than the first data rate, the second portion decodable by thesecond set of devices. In some aspects, the generating the secondportion includes generating an indication of scheduling information fora multi-user transmission. In some aspects, the generating the secondportion includes generating an identification of one or more of thesecond set of devices that will communicate during the multi-usertransmission. In some aspects, the generating the identification of theone or more of the second set of devices includes generating at leastone of a station identifier, group identifier, and associationidentifier for each of the one or more second set of devices.

In some aspects, the generating the second portion includes generatingan indication of one or more of a modulation and coding scheme (MCS),bandwidth, sub-band, spatial stream information, and length informationfor the multi-user transmission. In some aspects, the generating thefirst portion includes generating a duration field, the duration fieldincluding a data value greater than a combined length of the first andsecond portions.

In some aspects, the generating the second portion includes generatingan indication of a length of the second portion. In some aspects, thegenerating the first portion includes generating a signal field forindicating an end position of the second portion.

Another aspect disclosed is an apparatus for transmitting a physicallayer convergence protocol data unit on a wireless medium. In someaspects, the apparatus includes a processor configured to generate firstand second portions of the physical layer convergence protocol dataunit, a transmitter configured to transmit the first portion at a firstdata rate, the first portion decodable by a first and second sets ofdevices; and transmit the second portion at a second data rate higherthan the first data rate, the second portion decodable by the second setof devices. In some aspects, the generation of the second portionincludes generating an indication of scheduling information for amulti-user transmission. In some aspects, the generation of the secondportion includes generating an identification of one or more of thesecond set of devices that will communicate during the multi-usertransmission. In some aspects, the generation of the identification ofthe one or more of the second set of devices includes generating atleast one of a station identifier, group identifier, and associationidentifier for each of the one or more second set of devices.

In some aspects, the generation of the second portion includesgenerating an indication of one or more of a modulation and codingscheme (MCS), bandwidth, sub-band, spatial stream information, andlength information for the multi-user transmission. In some aspects, thegeneration of the first portion includes generating a duration fieldstoring a value greater than a combined length of the first and secondportions. In some aspects, the generation of the second portion includesgenerating an indication of a length of the second portion. In someaspects, the generation of the first portion includes generating asignal field indicating an end position of the second portion.

Another aspect disclosed is a method of receiving a physical layerconvergence protocol data unit on a wireless medium. The method includesreceiving, by a wireless device, a first portion of the physical layerconvergence protocol data unit, determining, based on the first portion,whether the physical layer convergence protocol data unit includes asecond portion transmitted at a higher data rate than the first portion;and receiving the second portion at the higher data rate based on thedetermining.

In some aspects, the method also includes decoding the second portionfor determining scheduling information for a multi-user transmission. Insome aspects, the method also includes decoding the second portion foridentifying one or more of the second set of devices that willcommunicate during the multi-user transmission, determining if thewireless device is identified, and communicating during the multi-usertransmission based on whether the wireless device is identified.

In some aspects, the method includes identifying the one or more of thesecond set of devices by decoding one of a station identifier, groupidentifier, and association identifier for each of the one or moresecond set of devices from the second portion. In some aspects, themethod includes decoding the second portion for determining one or moreparameters of the multi-user transmission including one or more of amodulation and coding scheme (MCS), bandwidth, sub-band, spatial streaminformation, and length information for the multi-user transmission; andperforming the multi-user transmission based on the determined one ormore parameters.

In some aspects, the method includes decoding the first portion fordetermining a duration field having a data value greater than a combinedlength of the first and second portions; and setting a networkallocation vector based on the data value of the duration field. In someaspects, the method also includes decoding an indication of a length ofthe second portion included in the second portion for determining thelength of the second portion; and decoding the second portion based onthe determined length.

In some aspects, the method also includes decoding a signal field in thefirst portion for determining an end position of the second portion; anddecoding the second portion based on the determined end position.

Another aspect disclosed is an apparatus for receiving a physical layerconvergence protocol data unit on a wireless medium. The apparatusincludes a receiver configured to receive a first portion of thephysical layer convergence protocol data unit; and a processorconfigured to determine, based on the first portion, whether thephysical layer convergence protocol data unit includes a second portiontransmitted at a higher data rate than the first portion, wherein thereceiver is further configured to receive the second portion at thehigher data rate based on the determining.

In some aspects of the apparatus, the processor is further configuredto: decode the second portion for determining scheduling information fora multi-user transmission. In some aspects, the processor is furtherconfigured to decode the second portion for identifying one or moredevices that will communicate during the multi-user transmission,determine if the apparatus is identified; and communicate during themulti-user transmission based on whether the apparatus is identified.

In some aspects of the apparatus, the processor is further configured toidentify the one or more of devices by decoding one of a stationidentifier, group identifier, and association identifier for each of theone or more second set of devices from the second portion. In someaspects of the apparatus, the processor is further configured to decodethe second portion for determining one or more parameters of themulti-user communication including a modulation and coding scheme (MCS),bandwidth, sub-band, spatial stream information, and length informationfor the multi-user transmission, and perform the multi-user transmissionbased on the determined parameters.

In some aspects of the apparatus, the processor is further configured todecode the first portion for determining a duration field having a datavalue greater than a combined length of the first and second portions;and set a network allocation vector based on the determined data valueof the duration field.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a multiple-access multiple-input multiple-output(MIMO) system with access points and user terminals.

FIG. 2 illustrates a block diagram of the access point 110 and two userterminals 120 m and 120 x in a MIMO system.

FIG. 3 illustrates various components that may be utilized in a wirelessdevice that may be employed within a wireless communication system.

FIG. 4 is a diagram that illustrates a multiple-access multiple-inputmultiple-output (MIMO) system 100 with access points and user terminals.

FIG. 5A illustrates an exemplary clear to send frame.

FIG. 5B illustrates an exemplary frame control field.

FIG. 6A illustrates an exemplary message for communicating multi-useruplink transmission information to both legacy and non-legacy devices.

FIG. 6B is an illustration of one embodiment of a second portion.

FIG. 6C is a simplified illustration of one embodiment of the PPDUdescribed in FIG. 6A.

FIG. 6D is a simplified illustration of one embodiment of the PPDUdescribed in FIG. 6A.

FIGS. 6E-H are simplified illustrations of embodiments of messageexchanges that include provisions for extending the response time for amulti-user uplink transmission.

FIG. 7 is an example of a second portion of a PPDU.

FIG. 8 illustrates another example of a second portion of a PPDU.

FIG. 9 is a message timing diagram for one implementation of multi-useruplink transmission.

FIG. 10A is a flowchart of a method for multi-user uplink communicationon a wireless network.

FIG. 10B is a functional block diagram of an apparatus for wirelesscommunication, in accordance with certain embodiments described herein.

FIG. 11A is a flowchart of a method for multi-user uplink communicationon a wireless network.

FIG. 11B is a functional block diagram of an apparatus for wirelesscommunication, in accordance with certain embodiments described herein.

DETAILED DESCRIPTION

Various aspects of the novel systems, apparatuses, and methods aredescribed more fully hereinafter with reference to the accompanyingdrawings. The teachings disclosure may, however, be embodied in manydifferent forms and should not be construed as limited to any specificstructure or function presented throughout this disclosure. Rather,these aspects are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the disclosure to thoseskilled in the art. Based on the teachings herein one skilled in the artshould appreciate that the scope of the disclosure is intended to coverany aspect of the novel systems, apparatuses, and methods disclosedherein, whether implemented independently of or combined with any otheraspect of the invention. For example, an apparatus may be implemented ora method may be practiced using any number of the aspects set forthherein. In addition, the scope of the invention is intended to coversuch an apparatus or method which is practiced using other structure,functionality, or structure and functionality in addition to or otherthan the various aspects of the invention set forth herein. It should beunderstood that any aspect disclosed herein may be embodied by one ormore elements of a claim.

Although particular aspects are described herein, many variations andpermutations of these aspects fall within the scope of the disclosure.Although some benefits and advantages of the preferred aspects arementioned, the scope of the disclosure is not intended to be limited toparticular benefits, uses, or objectives. Rather, aspects of thedisclosure are intended to be broadly applicable to different wirelesstechnologies, system configurations, networks, and transmissionprotocols, some of which are illustrated by way of example in thefigures and in the following description of the preferred aspects. Thedetailed description and drawings are merely illustrative of thedisclosure rather than limiting, the scope of the disclosure beingdefined by the appended claims and equivalents thereof.

Wireless network technologies may include various types of wirelesslocal area networks (WLANs). A WLAN may be used to interconnect nearbydevices together, employing widely used networking protocols. Thevarious aspects described herein may apply to any communicationstandard, such as Wi-Fi or, more generally, any member of the IEEE802.11 family of wireless protocols.

In some aspects, wireless signals may be transmitted according to ahigh-efficiency 802.11 protocol using orthogonal frequency-divisionmultiplexing (OFDM), direct-sequence spread spectrum (DSSS)communications, a combination of OFDM and DSSS communications, or otherschemes. Implementations of the high-efficiency 802.11 protocol may beused for Internet access, sensors, metering, smart grid networks, orother wireless applications. Advantageously, aspects of certain devicesimplementing this particular wireless protocol may consume less powerthan devices implementing other wireless protocols, may be used totransmit wireless signals across short distances, and/or may be able totransmit signals less likely to be blocked by objects, such as humans.

In some implementations, a WLAN includes various devices which are thecomponents that access the wireless network. For example, there may betwo types of devices: access points (“APs”) and clients (also referredto as stations, or “STAs”). In general, an AP serves as a hub or basestation for the WLAN and an STA serves as a user of the WLAN. Forexample, a STA may be a laptop computer, a personal digital assistant(PDA), a mobile phone, etc. In an example, an STA connects to an AP viaa Wi-Fi (e.g., IEEE 802.11 protocol such as 802.11ah) compliant wirelesslink to obtain general connectivity to the Internet or to other widearea networks. In some implementations an STA may also be used as an AP.

The techniques described herein may be used for various broadbandwireless communication systems, including communication systems that arebased on an orthogonal multiplexing scheme. Examples of suchcommunication systems include Spatial Division Multiple Access (SDMA),Time Division Multiple Access (TDMA), Orthogonal Frequency DivisionMultiple Access (OFDMA) systems, Single-Carrier Frequency DivisionMultiple Access (SC-FDMA) systems, and so forth. An SDMA system mayutilize sufficiently different directions to simultaneously transmitdata belonging to multiple user terminals. A TDMA system may allowmultiple user terminals to share the same frequency channel by dividingthe transmission signal into different time slots, each time slot beingassigned to different user terminal. A TDMA system may implement GSM orsome other standards known in the art. An OFDMA system utilizesorthogonal frequency division multiplexing (OFDM), which is a modulationtechnique that partitions the overall system bandwidth into multipleorthogonal sub-carriers. These sub-carriers may also be called tones,bins, etc. With OFDM, each sub-carrier may be independently modulatedwith data. An OFDM system may implement IEEE 802.11 or some otherstandards known in the art. An SC-FDMA system may utilize interleavedFDMA (IFDMA) to transmit on sub-carriers that are distributed across thesystem bandwidth, localized FDMA (LFDMA) to transmit on a block ofadjacent sub-carriers, or enhanced FDMA (EFDMA) to transmit on multipleblocks of adjacent sub-carriers. In general, modulation symbols are sentin the frequency domain with OFDM and in the time domain with SC-FDMA. ASC-FDMA system may implement 3GPP-LTE (3rd Generation PartnershipProject Long Term Evolution) or other standards.

The teachings herein may be incorporated into (e.g., implemented withinor performed by) a variety of wired or wireless apparatuses (e.g.,nodes). In some aspects, a wireless node implemented in accordance withthe teachings herein may comprise an access point or an access terminal.

An access point (“AP”) may comprise, be implemented as, or known as aNodeB, Radio Network Controller (“RNC”), eNodeB, Base Station Controller(“BSC”), Base Transceiver Station (“BTS”), Base Station (“BS”),Transceiver Function (“TF”), Radio Router, Radio Transceiver, BasicService Set (“BSS”), Extended Service Set (“ESS”), Radio Base Station(“RBS”), or some other terminology.

A station “STA” may also comprise, be implemented as, or known as a userterminal, an access terminal (“AT”), a subscriber station, a subscriberunit, a mobile station, a remote station, a remote terminal, a useragent, a user device, user equipment, or some other terminology. In someimplementations an access terminal may comprise a cellular telephone, acordless telephone, a Session Initiation Protocol (“SIP”) phone, awireless local loop (“WLL”) station, a personal digital assistant(“PDA”), a handheld device having wireless connection capability, orsome other suitable processing device connected to a wireless modem.Accordingly, one or more aspects taught herein may be incorporated intoa phone (e.g., a cellular phone or smartphone), a computer (e.g., alaptop), a portable communication device, a headset, a portablecomputing device (e.g., a personal data assistant), an entertainmentdevice (e.g., a music or video device, or a satellite radio), a gamingdevice or system, a global positioning system device, or any othersuitable device that is configured to communicate via a wireless medium.

FIG. 1 is a diagram that illustrates a multiple-access multiple-inputmultiple-output (MIMO) system 100 with access points and user terminals.For simplicity, only one access point 110 is shown in FIG. 1. An accesspoint is generally a fixed station that communicates with the userterminals and may also be referred to as a base station or using someother terminology. A user terminal or STA may be fixed or mobile and mayalso be referred to as a mobile station or a wireless device, or usingsome other terminology. The access point 110 may communicate with one ormore user terminals 120 at any given moment on the downlink and uplink.The downlink (i.e., forward link) is the communication link from theaccess point to the user terminals, and the uplink (i.e., reverse link)is the communication link from the user terminals to the access point. Auser terminal may also communicate peer-to-peer with another userterminal. A system controller 130 couples to and provides coordinationand control for the access points.

While portions of the following disclosure will describe user terminals120 capable of communicating via Spatial Division Multiple Access(SDMA), for certain aspects, the user terminals 120 may also includesome user terminals that do not support SDMA. Thus, for such aspects,the AP 110 may be configured to communicate with both SDMA and non-SDMAuser terminals. This approach may conveniently allow older versions ofuser terminals (“legacy” stations) that do not support SDMA to remaindeployed in an enterprise, extending their useful lifetime, whileallowing newer SDMA user terminals to be introduced as deemedappropriate.

The system 100 employs multiple transmit and multiple receive antennasfor data transmission on the downlink and uplink. The access point 110is equipped with N_(ap) antennas and represents the multiple-input (MI)for downlink transmissions and the multiple-output (MO) for uplinktransmissions. A set of K selected user terminals 120 collectivelyrepresents the multiple-output for downlink transmissions and themultiple-input for uplink transmissions. For pure SDMA, it is desired tohave N_(ap)≤K≤1 if the data symbol streams for the K user terminals arenot multiplexed in code, frequency or time by some means. K may begreater than N_(ap) if the data symbol streams can be multiplexed usingTDMA technique, different code channels with CDMA, disjoint sets ofsub-bands with OFDM, and so on. Each selected user terminal may transmituser-specific data to and/or receive user-specific data from the accesspoint. In general, each selected user terminal may be equipped with oneor multiple antennas (i.e., N_(ut)≥1). The K selected user terminals canhave the same number of antennas, or one or more user terminals may havea different number of antennas.

The SDMA system 100 may be a time division duplex (TDD) system or afrequency division duplex (FDD) system. For a TDD system, the downlinkand uplink share the same frequency band. For an FDD system, thedownlink and uplink use different frequency bands. The MIMO system 100may also utilize a single carrier or multiple carriers for transmission.Each user terminal may be equipped with a single antenna (e.g., in orderto keep costs down) or multiple antennas (e.g., where the additionalcost can be supported). The system 100 may also be a TDMA system if theuser terminals 120 share the same frequency channel by dividingtransmission/reception into different time slots, where each time slotmay be assigned to a different user terminal 120.

FIG. 2 illustrates a block diagram of the access point 110 and two userterminals 120 m and 120 x in MIMO system 100. The access point 110 isequipped with N_(t) antennas 224 a through 224 ap. The user terminal 120m is equipped with N_(ut,m) antennas 252 _(ma) through 252 _(mu), andthe user terminal 120 x is equipped with N_(ut,x) antennas 252 _(xa)through 252 _(xu). The access point 110 is a transmitting entity for thedownlink and a receiving entity for the uplink. The user terminal 120 isa transmitting entity for the uplink and a receiving entity for thedownlink. As used herein, a “transmitting entity” is an independentlyoperated apparatus or device capable of transmitting data via a wirelesschannel, and a “receiving entity” is an independently operated apparatusor device capable of receiving data via a wireless channel. In thefollowing description, the subscript “dn” denotes the downlink, thesubscript “up” denotes the uplink, N_(up) user terminals are selectedfor simultaneous transmission on the uplink, and N_(dn) user terminalsare selected for simultaneous transmission on the downlink. N_(up) mayor may not be equal to N_(dn), and N_(up) and N_(dn) may be staticvalues or may change for each scheduling interval. Beam-steering or someother spatial processing technique may be used at the access point 110and/or the user terminal 120.

On the uplink, at each user terminal 120 selected for uplinktransmission, a TX data processor 288 receives traffic data from a datasource 286 and control data from a controller 280. The TX data processor288 processes (e.g., encodes, interleaves, and modulates) the trafficdata for the user terminal based on the coding and modulation schemesassociated with the rate selected for the user terminal and provides adata symbol stream. A TX spatial processor 290 performs spatialprocessing on the data symbol stream and provides N_(ut,m) transmitsymbol streams for the N_(ut,m) antennas. Each transmitter unit (TMTR)254 receives and processes (e.g., converts to analog, amplifies,filters, and frequency upconverts) a respective transmit symbol streamto generate an uplink signal. N_(ut,m) transmitter units 254 provideN_(ut,m) uplink signals for transmission from N_(ut,m) antennas 252, forexample to transmit to the access point 110.

N_(up) user terminals may be scheduled for simultaneous transmission onthe uplink. Each of these user terminals may perform spatial processingon its respective data symbol stream and transmit its respective set oftransmit symbol streams on the uplink to the access point 110.

At the access point 110, N_(up) antennas 224 a through 224 _(ap) receivethe uplink signals from all N_(up) user terminals transmitting on theuplink. Each antenna 224 provides a received signal to a respectivereceiver unit (RCVR) 222. Each receiver unit 222 performs processingcomplementary to that performed by transmitter unit 254 and provides areceived symbol stream. An RX spatial processor 240 performs receiverspatial processing on the N_(up) received symbol streams from N_(up)receiver units 222 and provides N_(up) recovered uplink data symbolstreams. The receiver spatial processing may be performed in accordancewith the channel correlation matrix inversion (CCMI), minimum meansquare error (MMSE), soft interference cancellation (SIC), or some othertechnique. Each recovered uplink data symbol stream is an estimate of adata symbol stream transmitted by a respective user terminal. An RX dataprocessor 242 processes (e.g., demodulates, deinterleaves, and decodes)each recovered uplink data symbol stream in accordance with the rateused for that stream to obtain decoded data. The decoded data for eachuser terminal may be provided to a data sink 244 for storage and/or acontroller 230 for further processing.

On the downlink, at the access point 110, a TX data processor 210receives traffic data from a data source 208 for N_(dn) user terminalsscheduled for downlink transmission, control data from a controller 230,and possibly other data from a scheduler 234. The various types of datamay be sent on different transport channels. TX data processor 210processes (e.g., encodes, interleaves, and modulates) the traffic datafor each user terminal based on the rate selected for that userterminal. The TX data processor 210 provides N_(dn) downlink data symbolstreams for the N_(dn) user terminals. A TX spatial processor 220performs spatial processing (such as a precoding or beamforming) on theN_(dn) downlink data symbol streams, and provides N_(up) transmit symbolstreams for the N_(up) antennas. Each transmitter unit 222 receives andprocesses a respective transmit symbol stream to generate a downlinksignal. N_(up) transmitter units 222 may provide N_(up) downlink signalsfor transmission from N_(up) antennas 224, for example to transmit tothe user terminals 120.

At each user terminal 120, N_(ut,m) antennas 252 receive the N_(up)downlink signals from the access point 110. Each receiver unit 254processes a received signal from an associated antenna 252 and providesa received symbol stream. An RX spatial processor 260 performs receiverspatial processing on N_(ut,m) received symbol streams from N_(ut,m)receiver units 254 and provides a recovered downlink data symbol streamfor the user terminal 120. The receiver spatial processing may beperformed in accordance with the CCMI, MMSE, or some other technique. AnRX data processor 270 processes (e.g., demodulates, deinterleaves anddecodes) the recovered downlink data symbol stream to obtain decodeddata for the user terminal.

At each user terminal 120, a channel estimator 278 estimates thedownlink channel response and provides downlink channel estimates, whichmay include channel gain estimates, SNR estimates, noise variance and soon. Similarly, a channel estimator 228 estimates the uplink channelresponse and provides uplink channel estimates. Controller 280 for eachuser terminal typically derives the spatial filter matrix for the userterminal based on the downlink channel response matrix H_(dn,m) for thatuser terminal. Controller 230 derives the spatial filter matrix for theaccess point based on the effective uplink channel response matrixH_(up,eff). The controller 280 for each user terminal may send feedbackinformation (e.g., the downlink and/or uplink eigenvectors, eigenvalues,SNR estimates, and so on) to the access point 110. The controllers 230and 280 may also control the operation of various processing units atthe access point 110 and user terminal 120, respectively.

FIG. 3 illustrates various components that may be utilized in a wirelessdevice 302 that may be employed within the wireless communication system100. The wireless device 302 is an example of a device that may beconfigured to implement the various methods described herein. Thewireless device 302 may implement an access point 110 or a user terminal120.

The wireless device 302 may include a processor 304 which controlsoperation of the wireless device 302. The processor 304 may also bereferred to as a central processing unit (CPU). Memory 306, which mayinclude both read-only memory (ROM) and random access memory (RAM),provides instructions and data to the processor 304. A portion of thememory 306 may also include non-volatile random access memory (NVRAM).The processor 304 may perform logical and arithmetic operations based onprogram instructions stored within the memory 306. The instructions inthe memory 306 may be executable to implement the methods describedherein.

The processor 304 may comprise or be a component of a processing systemimplemented with one or more processors. The one or more processors maybe implemented with any combination of general-purpose microprocessors,microcontrollers, digital signal processors (DSPs), field programmablegate array (FPGAs), programmable logic devices (PLDs), controllers,state machines, gated logic, discrete hardware components, dedicatedhardware finite state machines, or any other suitable entities that canperform calculations or other manipulations of information.

The processing system may also include machine-readable media forstoring software. Software shall be construed broadly to mean any typeof instructions, whether referred to as software, firmware, middleware,microcode, hardware description language, or otherwise. Instructions mayinclude code (e.g., in source code format, binary code format,executable code format, or any other suitable format of code). Theinstructions, when executed by the one or more processors, cause theprocessing system to perform the various functions described herein.

The wireless device 302 may also include a housing 308 that may includea transmitter 310 and a receiver 312 to allow transmission and receptionof data between the wireless device 302 and a remote location. Thetransmitter 310 and receiver 312 may be combined into a transceiver 314.A single or a plurality of transceiver antennas 316 may be attached tothe housing 308 and electrically coupled to the transceiver 314. Thewireless device 302 may also include (not shown) multiple transmitters,multiple receivers, and multiple transceivers.

The wireless device 302 may also include a signal detector 318 that maybe used in an effort to detect and quantify the level of signalsreceived by the transceiver 314. The signal detector 318 may detect suchsignals as total energy, energy per subcarrier per symbol, powerspectral density and other signals. The wireless device 302 may alsoinclude a digital signal processor (DSP) 320 for use in processingsignals.

The various components of the wireless device 302 may be coupledtogether by a bus system 322, which may include a power bus, a controlsignal bus, and a status signal bus in addition to a data bus.

Certain aspects of the present disclosure support transmitting an uplink(UL) signal from multiple STAs to an AP. In some embodiments, the ULsignal may be transmitted in a multi-user MIMO (MU-MIMO) system.Alternatively, the UL signal may be transmitted in a multi-user FDMA(MU-FDMA) or similar FDMA system. In some embodiments, UL-MU-MIMO orUL-FDMA transmissions can be sent simultaneously from multiple STAs toan AP and may create efficiencies in wireless communication.

FIG. 4 is a diagram that illustrates a multiple-access multiple-inputmultiple-output (MIMO) system 100 with access points and user terminals.The access point 110 in FIG. 4 is shown communicating with two groups ofdevices 402 a-b. The first group of devices 402 a includes at least userterminals 120 a-c. The second group of devices 402 b includes at leastuser terminals 120 d-f. In some aspects, user terminals 120 a-c may havea first set of features or capabilities, while user terminals 120 d-fmay have a second set of capabilities or features. For example, userterminals 120 a-c may have been manufactured before a particular date,and thus their features or capabilities reflect technical standards andor features present at their time of manufacture. In contrast, userterminals 120 d-f may have been manufactured after the particular date,and thus their features or capabilities include implementation oftechnical standards and/or features that post-date the particular date.Alternatively, user terminals 120 a-c may be less sophisticated and thusless expensive devices than user terminals 120 d-f. Due to lessexpensive design, user terminals 120 a-c may be able to provide fewerfeatures and/or capabilities than user terminals 120 d-f.

As discussed above, certain aspects of the present disclosure supporttransmitting an uplink (UL) signal from multiple STAs to an accesspoint. Older, legacy devices may not implement multi-user uplinktransmissions. Therefore, network messages implementing multi-useruplink transmissions that were defined after the older legacy deviceswere produced, may not be readily interpreted or decoded by these legacydevices. However, it is still desirable to have these legacy devicesrefrain from transmissions during a non-contention period associatedwith multi-user uplink (UL) transmissions. One way to accomplish thiswould be to transmit two separate PPDUs, with a first PPDU indicating tolegacy devices that they should refrain from transmission during acontention free period. A second, separate transmission of a PPDU couldthen be performed to communicate parameters of a multi-user transmissionto select devices that have multi-user uplink capabilities. However, thetransmission of two separate messages for the two sets of devicespresents inefficiencies in network operation that are undesirable. Thus,methods and systems that communicate contention free periods to alldevices, including legacy devices, in an efficient manner are desired,even when the contention free period will be used for multi-user uplinktransmissions.

Additionally, devices that are capable of performing multi-usertransmissions may also possess additional capabilities beyond those oflegacy devices. For example, some of these devices may be capable oftransmitting and/or receiving data at higher data rates than legacydevices. Therefore, it is desirable to take advantage of highertransmission and/or receive data rates present in modern devices toimprove network throughput.

FIG. 5A illustrates an exemplary clear to send frame. The clear to sendframe 500 includes a physical layer convergence protocol (PLCP) header501 and a Media Access Control Protocol Data Unit (MPDU) 503. The PLCPheader 501 includes at least a short training field 502, a long trainingfield 504, and a signal field 506. The Media Access Control ProtocolData Unit (MPDU) 503 includes a data portion 508, that includes aservice field 510, a physical layer service data unit 512, a tail field514, and a pad field 516. The service field 510 includes a scramblerseed field 522 and other fields 524. The physical layer service dataunit field 512 includes a frame control field 532, duration field 534,address field 536, and a frame check sequence field 538.

FIG. 6A illustrates an exemplary message for communicating multi-useruplink transmission information to both legacy and non-legacy devices.The example message 600 includes fields corresponding to those describedwith respect to FIG. 5A. In some aspects, frame control field 632 maysubstantially conform with the format shown for frame control field 532in FIG. 5B. In addition, the message 600 includes two data portions,MPDU 603, shown as data portion 608, and also a second data portion 609.Data portion 608 is equivalent to data 508 described with respect toFIG. 5A. This equivalency enables data portion 608 to be decoded by bothlegacy and non-legacy devices. Data portion 609 may be formatted in amanner that is not decodable by legacy devices. For example, the formatof data portion 609 may not have been defined with some legacy deviceswere designed and/or produced. In some aspects, data portion 609 may betransmitted at a different data rate than data portion 608, and also ata higher rate than the first portion should in FIG. 6A, which includesthe PLCP Header 601 and data portion 608. In some aspects, legacydevices may not be able to decode data portion 609 because of its higherdata transmission rate.

In some aspects, data portion 609 may comprise information such asdownlink data for specific receivers. In some aspects, data portion 609may start with or include a Group ID that identifies a group of STAs towhich a subsequent portion of data portion 609 is addressed. In someaspects, the presence of data portion 609 in frame 600 may be signaledto a device receiving frame 600. This signaling may be designed to notinterfere with legacy devices decoding and processing of the firstportion 600 a. For example, in some aspects, a transmitter of frame 600may set the address field 636 of data portion 608 based on whether thesecond portion 609 is present in a frame. When transmitting frame 500 ofFIG. 5A, a transmitting device may set the address field 536 to a basicservice set identifier (BSSID) of the transmitting device. Whentransmitting frame 600, which includes second portion 609, thetransmitting device may set the address field 636 to a multicast versionof the basic service set identifier (BSSID). A receiving device decodingthe address field 536 and/or 636 may determine whether the address is amulticast address or not. If the field 536 and/or 636 is multicast, areceiving device may determine data portion 609 is present in the frame,while if the address is not multicast, the receiving device maydetermine data portion 609 is not present (i.e. a frame similar to frame500 is being received). Other fields of frames 500 and 600 may be usedto indicate whether the second portion 609 is present in a frame. Forexample, in some aspects, a frame subtype field (not shown) in the framecontrol field 632 may indicate whether the second portion 609 ispresent. In some aspects, a specific combination of frame type andsubtype field (not shown) in the frame control field 632 may indicatewhether the second portion 609 is present. In some aspects, a specificcontrol subtype may indicate whether the second portion 609 is present.In some aspects, a specific control frame extension may indicate whetherthe second portion 609 is present. In some aspects, a specific extensionsubtype may indicate whether the second portion 609 is present. In someaspects, a specific control frame, control frame extension frame, orextension frame indicating the presence of second portion 609 maycomprise the same subfields as a CTS MPDU (i.e. Frame Control, Duration,Address, FCS). In some aspects, the scrambler seed field 522 and/or 622may indicate the presence of the second portion 609. In some aspects, acombination of a multicast version of the BSSID and a specific value of(part of) the scrambler seed may indicate the presence of the secondportion 609. In some aspects, instead of a multicast version of theBSSID a localized version of the BSSID may be used. In some aspects, theL-SIG field 506/606 may indicate the presence of the data portion 609.For example, in some aspects, if the L-SIG field 506/506 indicates alength that is longer than the PLCP header 601 and first portion 608, areceiver may determine that the second portion 609 is present.

In some aspects, setting particular bits of the Frame Control (FC) field632 included in the PSDU 612 may indicate the presence of the secondportion 609. In some aspects, setting to one (1) one of the followingsubfields of the FC field 632 may indicate the presence of the secondportion 609: To DS field (such as field 556 of FIG. 5B), From DS field(such as field 558 of FIG. 5B), More Frag field (such as field 560 ofFIG. 5B), Retry field (such as field 562 of FIG. 5B), or a ProtectedFrame field (such as field 568 of FIG. 5B). In some aspects, if acombination of these subfields are set to one (1), the frame controlfield 632 may indicate the presence of second portion 609. In someaspects, a combination of these subfields set to one (1) in combinationwith particular values of a multicast address field 636 may indicate thepresence of second portion 609. In some aspects, a specific value in thescrambler seed field 622 may also be used in conjunction with the fieldsdiscussed above to indicate that second portion 609 is present. In someaspects, the second portion 609 contains a second portion type field(not shown), which indicates a type of the second portion 609. In someaspects, the PSDU 612 may be a clear-to-send frame.

FIG. 6B is an illustration of one embodiment of a second portion 609 a.In some aspects, second portion 609 a may start with or include agreenfield VHT PHY header preceding a downlink MU-MIMO transmission. Agreenfield VHT PHY header is a VHT PHY header without a legacy OFDMportion 699, i.e. a VHT PHY header that starts at VHT SIG-A field 688and omits the L-STF 682, L-LTF 684 and L-SIG 686 fields of the VHT PHYheader. In some aspects, second portion 609 a may comprise a modifiedgreenfield VHT PHY header, which includes uplink (multi-user)transmission information. The uplink (multi-user) transmission may beginafter the downlink VHT transmission, for example separated by a SIFSinterval.

FIG. 6C is a simplified illustration of one embodiment of the PLCPProtocol Data Unit 600 described in FIG. 6A. As shown, the PPDU 650includes a signal field 606, a MPDU 608, and a second portion 609. Inthe aspect shown in FIG. 6C, the L-SIG value defines a length of theMPDU 608, which in this case is a clear-to-send frame that is fourteen(14) bytes long. Since the signal field 606 is indicating a lengthequivalent to the length of the MPDU 608 (in this case a clear-to-sendframe), a device receiving the PPDU 650 may determine whether the secondportion 609 is present in the PPDU 650 based on some other field besidesthe signal field 606. For example, as discussed above, one or more of asubtype field, scrambler seed field, and/or address field may be used todetermine whether the second portion 609 is present in the PPDU 650.

FIG. 6D is a simplified illustration of one embodiment of the PLCPProtocol Data Unit 600 described in FIG. 6A. As shown, the PLCP ProtocolData Unit 675 includes a signal field 606, a MPDU 608, and a secondportion 609. In the aspect shown in FIG. 6D, the L-SIG value defines alength of the MPDU 608 which in this case is a clear-to-send frame thatis fourteen (14) bytes long, plus an additional amount “z.” The combinedlength of the MPDU (14) and the amount “z” indicates the transmissiontime of the PPDU 675 extends to the end of second portion 609. A devicereceiving the PLCP Protocol Data Unit 675 may determine whether thesecond portion 609 is present in the PPDU 675 based on the L-SIG field606. For example, if the L-SIG filed 606 indicates a length greater thanthe length of the MPDU 608, a receiving device may determine the secondportion 609 is present in the PPDU 675.

In some aspects, the network allocation vector (NAV) indicated in PPDU675 is to be set after a time indicated by the L-SIG value. For example,the PPDU 675 may indicate that the NAV starts after completion of thetransmission of the PPDU 675, including both the first portion 608 andsecond portion 609.

In some aspects, the first portion 608 may indicate a NAV that extendsbeyond the length of the second portion, as shown in FIG. 6D. In someaspects, the first portion 608 may indicate that a multi-usertransmission will be performed after transmission of the second portion609. The NAV indicated by the first portion 608 may provide protectionfor the multi-user transmission. In some aspects, the length of thesecond portion 609 is indicated by the second portion itself. Forexample, the second portion 609 may include a length field, perhapsearly in the second portion, such that decoding devices can determinethe length of the second portion. In some aspects, the L-SIG value 606may indicate the length of the second portion as discussed above. Insome other aspects, the length of the second portion may bepredetermined. For example, in some aspects, the length of the secondportion may be fixed. In some other aspects, the length of the secondportion may be communicated to one or more receivers via separatemessage exchanges (not shown).

FIGS. 6E-H are simplified illustrations of embodiments of messageexchanges that include provisions for extending the response time for amulti-user uplink transmission.

FIG. 6E illustrates a message exchange 690. The PPDU transmitted as partof message exchange 690 includes an signal field 606 that indicates thelength of the CTS MPDU 608. Extra symbols 680 are transmitted after thesecond portion 609. In some aspects, the extra symbols 680 may betransmitted after a cyclic redundancy check field or a frame checksequence field of the second portion 609. The presence of these extrasymbols 680 is known by devices that will perform an uplink transmissionduring the transmission opportunity 682. The presence of the extrasymbols 680 enables the uplink transmitting devices to postpone theiruplink transmissions until transmission of the extra symbols have beencompleted, and after the short inter-frame space (SIFS) time 681 haspassed. This additional time between completion of the transmission ofsecond portion 609 and the beginning of an uplink transmission mayprovide additional time for Phased Locked Loops (PLLs) to settle at theuplink transmitters.

FIG. 6F illustrates an alternate message exchange 692. Message exchange692 does not transmit the extra symbols 680 of FIG. 6E. Instead oftransmitting extra symbols 680 and maintaining a consistent shortinter-frame space SIFS time 681, message exchange 692 utilizes anextended short inter-frame space (SIFS) time 683. The extended shortinter-frame space time 683 functions in a similar manner as the extrasymbols and SIFS 681, in that it provides additional time after thetransmission/reception of second portion 609 before an uplinktransmission during TxOp 684 begins. In some aspects, the extended SIFStime may or may not be filled with extra (random) symbols. As discussedabove, this additional time may provide for Phased Locked Loops (PLLs)to settle at uplink transmitters.

FIG. 6G also illustrates the use of extra symbols 680 during a messageexchange 694. Message exchange 694 differs from message exchange 690 inthat the signal field 606 of FIG. 6G may be followed by a CTX MPDU608-ctx instead of a CTS MPDU 608 as illustrated in FIG. 6E. In someaspects, the extra symbols may be transmitted after a cyclic redundancycheck field or a frame check sequence field of the CTX MPDU 608-ctx.

FIG. 6H illustrates a message exchange 696 including a CTX MPDU 608ctxthat utilizes an extended SIFS time 683, instead of the extra symbols680 as described above with respect to FIG. 6G. In some aspects, theextended SIFS time may or may not be filled with extra (random) symbols.

FIG. 7 is an example of a second portion 609 b of a PLCP Protocol DataUnit. The second portion includes a control (CTRL) field 720, a PLCPProtocol Data Unit duration field 725, a STA info field 730 a-n, and anerror check field 780. The CTRL field 720 is a generic field that mayinclude information regarding the format of the remaining portion of theframe (e.g., the number of STA info fields and the presence or absenceof any subfields within a STA info field), indications for rateadaptation for the user terminals 120, and/or an indication of allowedTID. The CTRL field 720 may also indicate if the multi-user transmissionthat follows the frame 600 is being used for UL MU MIMO or for UL FDMAor both, indicating whether a Nss or Tone allocation field is present inthe STA Info field 1230. Alternatively, the indication of whether frame600 is for UL MU MIMO or for UL FDMA can be based on the value of asubtype field in the frame control field 632, for example, as shown withrespect to frame control field 532 of FIG. 5B, which includes a sub-typefield 554. Note that UL MU MIMO and UL FDMA operations can be jointlyperformed by specifying to a STA both the spatial streams to be used andthe channel to be used, in which case both fields are present in thesecond portion; in this case, the Nss indication is referred to aspecific tone allocation. The PPDU duration 725 field indicates theduration of the following UL-MU-MIMO PPDU that the user terminals 120are allowed to send. The STA Info fields 730 a-n contain informationregarding a particular STA and may include a per-STA (per user terminal120) set of information (see STA Info 1 730 a and STA Info N 730 n). TheSTA Info fields 730 a-n may include an AID or MAC address field 732which identifies a STA, a number of spatial streams field (Nss) 734field which indicates the number of spatial streams a STA may use (in anUL-MU-MIMO system), a Time Adjustment field 736 which indicates a timethat a STA should adjust its transmission compared to the reception of atrigger frame (frame 600 in this case), a Power Adjustment field 738which indicates a power back-off a STA should take from a declaredtransmit power, a Tone Allocation field 740 which indicates the tones orfrequencies a STA may use (in a UL-FDMA system), an Allowed TID 742field which indicates the allowable TID, an Allowed TX Mode 744 fieldwhich indicates the allowed TX modes. A user terminal 120 receiving asecond portion 609 with an Allowed TID 742 indication may be allowed totransmit data only of that TID, data of the same or higher TID, data ofthe same or lower TID, any data, or only data of that TID first, then ifno data is available, data of other TIDs.

FIG. 8 illustrates another example of a second portion 609 c of a PPDU.In this embodiment, the STA Info field 830 does not contain the AID orMAC Address field (such as field 732) and instead the second portion 609includes a group identifier (GID) 826 field which identifies the STAs bya group identifier rather than an individual identifier.

FIG. 9 is a message timing diagram for one implementation of multi-useruplink transmission. The diagram begins with the AP 110 transmittingPPDU 600 of FIG. 6A, which includes a first portion 608 and a secondportion 609. In some aspects, the first portion may define a contentionfree period on the wireless medium. For example, in some aspects, thefirst portion may be a clear-to-send frame. The first portion may beconfigured such that it can be readily decoded by both legacy andnon-legacy devices. For example, the first portion may be decodable byboth the devices in device set 402 a and device set 402 b illustrated inFIG. 4. Therefore, the STAs 120 a and 120 d-f shown in FIG. 9 can decodethe first portion 608. In some aspects, the decodability of firstportion 608 relates to its format. For example, in some aspects, boththe first and second sets of devices are configured to decode theallocation and values of fields comprising the first portion. In someaspects, the decodability of the first portion 608 relates to a rate atwhich the AP 110 transmits the first portion. For example, in someaspects, the first portion 608 may be transmitted at 6 Mbps OFDM. Insome aspects, all of STAs 120 a and 120 d-f may be able to decode framestransmitted at this rate. In some aspects, the first portion may bedecoded by the STA 120 a and STAs 120 d-f to indicate how to set anetwork allocation vector, which defines a contention free period 920 onthe wireless medium.

The second portion 609 may not be decodable by both the first and secondgroups of devices illustrated in FIG. 4. For example, the second portion609 may be decodable only by the group of devices in group 402 b. Insome aspects, the second portion 609 is transmitted by the AP 110 at ahigher data rate than the first portion 608. For example, in someaspects, the second portion 609 is transmitted at 12 or 24 Mbps. In someaspects, transmission of the second portion at this rate is conditionalon whether intended recipients of the second portion (in this case, STAs120 d-f) are near enough to be able to receive frames transmitted at thehigher rate.

When the second portion 609 is transmitted at a higher rate, STA 120 amay not be able to decode the second portion 609. However, thetransmission of second portion 609 does not interfere with STA 120 a'sability to decode the first portion 608. Therefore, STA 120 a is stillable to set its NAV as shown by NAV 920.

As discussed above with respect to FIGS. 7 and 8, the second portion mayinclude information defining how a multi-user uplink transmissionperformed during non-contention period 920 will be performed. Forexample, the second portion may indicate to one or more of STAs 120 d-fthat they may perform a multi-user transmission during thenon-contention period 920 and which multi-user parameters control thetransmission (such as which tones should be used in an UL-OFDMtransmission or the number of spatial streams used in a UL-MU-MIMOtransmission). In some aspects, scheduling information controlling themulti-user transmission included in the second portion may include anindication of one or more stations that should participate in the OFDMAand/or MU-MIMO multi-user transmission (such as station identifiers, MACaddresses, association identifiers, group identifiers, etc). Thescheduling information may also define one or more of bandwidth and/orsubband information for each device transmitting during the multi-usertransmission, how many spatial streams should be included in themulti-user transmission, and/or which device is assigned to whichspatial stream, the modulation and coding scheme (MCS) for themulti-user transmission, and the maximum length of the multi-usertransmission.

Stations receiving the second portion may then decode the second portionto decode one or more of the scheduling parameters controlling themulti-user transmission, and perform the multi-user transmission asspecified by the decoded parameters.

In the illustrated message sequence of FIG. 9, the second portionindicates to each of STAs 120 d-f that they should transmit during thecontention free period 920. After the PPDU 600 is transmitted, STA 120 adefers any pending transmissions during the contention free period 920.Since each of STAs 120 d-f was provided with an indication to transmitby the second portion 609, each of STAs 120 d-f transmits data 910 a-cduring the contention free period 920. Each of data transmissions 910a-c is based on multi-user uplink transmission parameters provided bythe second portion 609.

FIG. 10A is a flowchart of a method for multi-user uplink communicationon a wireless network. In some aspects, the method 1000 may be performedby the AP 110 and/or the wireless device 302. FIG. 10A describes amethod of controlling a multi-user uplink transmission on a wirelessmedium that is compatible with devices capable of multi-user uplinktransmissions and also with devices that may not be configured tooperate in a multi-user uplink environment. For example, legacy devicesmay not have programming logic so as to decode and properly interpretmulti-user control data, such as that described above with respect tothe second portion 609. By transmitting a physical layer convergenceprotocol data unit that includes two portions, compatibility with bothlegacy devices, and devices that support multi-user uplink transmissionsmay be achieved.

In block 1005, first and second portions of a physical layer convergenceprotocol data unit are generated. In some aspects, the first portion isgenerated to indicate a duration of a contention free period on thewireless medium. For example, in some aspects, the first portionincludes a clear-to-send frame.

In some aspects, the first portion is generated to indicate the presenceof the second portion in the PPDU. In some aspects, the first portion isgenerated to include a signal field storing a value indicating a lengthgreater than a length of the first portion. For example, in someaspects, the L-SIG field 606 of PPDU 600 may be generated to store avalue indicating a length greater than the length of first portion 608.In some aspects, the first portion is generated to include a durationfield, the duration field indicating a length greater than a length ofthe first portion. This may indicate to receiving devices that thesecond portion is present in some aspects.

In some aspects, a specific value greater than the length of firstportion 608 may be used to indicate the presence of a second portion 609in the physical layer convergence protocol data unit. For example, insome aspects, a length value of 0xFFFF may indicate the presence of thesecond portion.

In some aspects the first portion may be generated to include ascrambler seed value, with the scrambler seed value indicating thepresence or absence of the second portion. For example, in some aspects,scrambler seed field 622 may be generated with a value that indicatesthe presence or absence of the second portion. In some aspects, thescrambler seed value is used in combination with the L-SIG fielddescribed above to indicate the presence or absence of the secondportion.

In some aspects, the first portion may be generated to include a typefield and a subtype field. For example, the frame control field 632 mayinclude a type and subtype field, for example, as shown with respect toframe control field 532 of FIG. 5B, which includes a type field 552 andsub-type field 554. In some aspects, the subtype field 554 may begenerated with a value that indicates the presence or absence of thesecond portion.

In some aspects, the first portion may be generated to set one or morecombinations of fields in a frame control field, such as frame controlfield 632 illustrated in FIG. 6A, to indicate whether a second portionis present. For example, one or more of a “To DS” field, “From DS”field, “More Frag” field, “Retry” field, or “Protected Frame” field maybe generated to have a value of one (1) to indicate the second portionis present, while generating the frame control field to have one or moreof these fields with a value of zero (0) may indicate a second portionis not present.

In some aspects, one or more fields of a frame control field, along withone or more of a scrambler seed field, such as scrambler seed field 622,and/or an address field, such as address field 636 may be generated toindicate whether the second portion is present. For example, if theaddress field 636 is generated to indicate a multicast address, and oneor more particular fields of the frame control field 632 are generatedto have a value of one (1), this may indicate that the second portion ispresent in some aspects.

In some aspects, the first portion may be generated to include anaddress field, such as address field 636. In some aspects, the addressfield may be generated to include a value that indicates the presence orabsence of the second portion. For example, in some aspects, whether theaddress field includes a multicast address or a non-multicast addressmay indicate whether the second portion is present in the physical layerconvergence protocol data unit. In some aspects, whether the addressfield includes a localized address or a non-localized address mayindicate whether the second portion is present in the physical layerconvergence protocol data unit.

In some aspects, the second portion is generated to include an errorcheck value for the second portion. For example, in some aspects, thesecond portion may be generated to include a parity bit and/or cyclicredundancy check (CRC) value for the second portion.

In some aspects, the second portion is generated to indicate controldata for a multi-user uplink transmission. For example, the secondportion may be generated to identify a plurality of devices. In someaspects, the plurality of devices are each identified by their stationaddress or their association identifier. In some aspects, the secondportion may specify a group identifier, which identifies a group ofdevices that may perform a multi-user uplink transmission followingtransmission of the first and second portions.

In some aspects, the second portion is also generated to indicate aplurality of indications of multi-user transmission opportunitiescorresponding to each of the association identifiers. For example, foreach device identified in the second portion as performing a portion ofthe multi-user uplink transmission, transmission parameters for thatdevice's transmission may be included in the second portion. Asdescribed with respect to FIGS. 7 and 8, transmission parameters such astone allocations (field 740 and 840) and/or the number of spatialstreams (fields 734 and 834) may be indicated in the second portion.Other fields shown in the embodiment of second portions 609 a-c of FIGS.6B, 8, or 9 may be included in the second portion. In some aspects, thesecond portion may include multi-user transmission schedulinginformation such as bandwidth and/or subband assignments for one or moreof the devices participating in the defined multi-user communication,how many spatial streams will be utilized by the multi-usertransmission, the modulation and coding scheme (MCS) to be used by eachdevice participating in the multi-user transmission and/or the length ofthe multi-user transmission.

In block 1010, the first portion is transmitted at a first data rate. Asdiscussed above with respect to FIG. 9, the first portion is configuredand transmitted to be decodable by both a first and second sets ofdevices. For example, the first portion may be decodable by legacydevices that are not configured to support multi-user uplinktransmissions. The first portion may be transmitted at a data ratedecodable by these legacy devices. For example, the first portion may betransmitted at six (6) Mbps OFDM.

In block 1015, the second portion is transmitted at a second data ratehigher than the first data rate. The second portion is configured andtransmitted such that it may be decoded by a second set of devices. Thesecond set of devices and the first set of devices do not overlap. Insome aspects, the second portion is transmitted at 12 or 24 Mbps.

Some aspects of process 1000 also include receiving a network message.The network message may indicate the data rate at which the secondportion and/or the first portions should be sent. In some aspects thefirst and/or second portions are then transmitted at the appropriatedata rate(s) indicated by the network message. In some aspects, thenetwork message is received from an access point or a station. In someaspects, the received network message is a management frame.

In some aspects, process 1000 includes transmitting one or moreadditional symbols after transmission of the second portion. In someaspects, the additional symbols may be transmitted after a CRC or FCScovering the second portion is transmitted (as part of the secondportion at least in some aspects). In some aspects, these additionalsymbols provide time for a receiving device's phase locked loop (PLL) tosettle before a multi-user uplink transmission begins. In some aspects,the additional symbols may contain no information that needs to bereceived by any devices that will perform a multi-user uplinktransmission during the upcoming transmission opportunity. In someaspects, the additional symbols are transmitted to contain random data.In some aspects, a multi-user uplink transmission is then received shortinter-frame space time (SIFS) after transmission of the additionalsymbols completes.

In some other aspects, process 1000 includes receiving a multi-useruplink transmission after an extended short inter-frame space (SIFS)time that is longer than the standard SIFS time. This extended SIFS timealso provides additional PLL (Phase locked Loop) settlement time for adevice performing a multi-user uplink transmission during thetransmission opportunity following the extended SIFS.

FIG. 10B is a functional block diagram of an apparatus 1050 for wirelesscommunication, in accordance with certain embodiments described herein.In some aspects, the apparatus 1050 is the device 302. Those skilled inthe art will appreciate that the apparatus 1050 may have more componentsthan the simplified block diagrams shown in FIG. 10B. FIG. 10B includesonly those components useful for describing some prominent features ofimplementations within the scope of the claims.

The apparatus 1050 comprises a PLCP Protocol Data Unit generationcircuit 1055. In some aspects, the PLCP Protocol Data Unit generationcircuit 1055 may be configured to perform one or more of the functionsdescribed above with respect to block 1005. In some aspects, the PLCPProtocol Data Unit generation circuit 1055 may include the processor304. The apparatus 1050 further comprises a transmission circuit 1060.In some aspects, the transmission circuit 1060 may be configured toperform one or more of the functions described above with respect toblock 1010 and/or 1015. In some aspects, the transmission circuit 1060may include the transmitter 310.

FIG. 11A is a flowchart of a method for multi-user uplink communicationon a wireless network. In some aspects, the method 1100 may be performedby the stations 120 d-f illustrated in FIG. 4 and/or FIG. 9, and/or thewireless device 302. FIG. 11A describes a method of receiving controlinformation for a multi-user uplink transmission on a wireless mediumthat is compatible with devices that may not be configured to operate ina multi-user uplink environment. For example, a first set of devices,such as legacy devices, may not have hardware and/or programming logicso as to decode and properly interpret multi-user uplink transmissioncontrol data, such as that described above with respect to the secondportion 609. By first receiving a first portion of a physical layerconvergence protocol data unit that is decodable by a first and secondsets of devices, certain information relating to a non-contention periodmay be received by both a first and second sets of devices (for example,legacy and non-legacy devices). For example, a duration of anon-contention period may be determined from the first portion such thata network allocation vector may be properly set by both the first andsecond sets of devices operating on the wireless medium. For example,the first portion may be decoded by the first and second sets of devicesas a clear-to-send frame, which is understood by these devices to set aduration of a network allocation vector that defines a non-contention orcontention free period on the wireless network. In some aspects, thevalue of the duration field may indicate to a receiving device whetherthe second portion is present in the received frame. For example, if theduration field stores a value that is greater than a threshold, it mayindicate the second portion is present. Alternatively, if the durationfield stores a value that is greater than a length of the first portionplus an additional threshold then it may indicate the second portion ispresent. Correspondingly, if the duration field does not exceed theparameters discussed above then the duration field may indicate nosecond portion is present.

Those devices capable of multi-user uplink transmissions (for example,the second set of devices discussed above) may then receive and decode asecond portion of the PPDU that includes control information relating tothe multi-user uplink transmission to occur during the contention freeperiod. The second set of devices may be configured to determine whetherthe second portion is present in the PPDU based on one or more fields ofthe first portion, as discussed above and below.

The second portion may also be sent at a different data rate than thefirst portion because, in some aspects, the second set of devices haveimproved receive capabilities relative to the first set of devices. Thisimproved set of capabilities may include the ability to receive data ata higher data rate(s) than can be supported by the first set of,possible legacy, devices. Transmitting/receiving the second portion at ahigher data rate may improve network utilization and efficiency. Whilemethod 1100 is illustrated as including several blocks, it should beunderstood that not all blocks are performed in all aspects of method1100.

In block 1105, a first portion of a PLCP Protocol Data Unit is receivedby a first device at a first data rate. In some aspects, the firstdevice is a station, such as any of stations 120 d-f discussed above. Inblock 1110, the first portion is decoded to determine a duration of acontention free period. For example, as discussed above with respect toFIG. 9, the first portion may be decoded to set a network allocationvector, which defines a contention free period 920. In some aspects, thefirst portion is decoded as a clear-to-send frame.

In block 1115, the first portion is decoded to determine whether asecond portion of the PPDU is present. In some aspects, a signal field,such as signal field 606 is decoded for determining the presence of thesecond portion. For example, if the signal field indicates a length ofthe PPDU that is greater than the length of the first portion, process1100 may determine that the second portion is present. Alternatively, ifthe length indicated by the signal field is a specific value, with thespecific value also being greater than the length of the first portion,then process 1100 may determine the second portion is present. In someaspects, a duration field of the first portion may be decoded fordetermining whether the second portion is present. For example, if theduration field is greater than a threshold, the second portion may bedetermined to be present. Alternatively, if the duration field stores avalue that is greater than a length of the first portion and anadditional threshold or offset period of time then the duration mayindicate the second portion is present. Correspondingly, if the durationfield does not exceed the parameters discussed above then the durationfield may indicate no second portion is present.

In some aspects, a scrambler seed value, such as scrambler seed 622illustrated in

FIG. 6A may be decoded for determining whether the second portion ispresent. For example, if particular bits or combinations of bits are setto particular values, process 1100 may determine the second portion ispresent. In some aspects, a combination of particular scrambler seedvalues and signal field values may be used for determining whether thesecond portion is present.

In some aspects, a control frame included in the first portion mayinclude a frame control field, the frame control field defining a typefield and a subtype field. In some aspects, specific values of thesubtype field may indicate the presence or absence of the second portionin the PPDU. In some aspects, one or more combinations of fields in aframe control field, such as frame control field 632 illustrated in FIG.6A, may be decoded for determining whether a second portion is present.For example, one or more of a “To DS” field, “From DS” field, “MoreFrag” field, “Retry” field, or “Protected Frame” field may be decodedfor determining whether the second portion is present. In some aspects,one or more fields of a frame control field, along with one or more of ascrambler seed field, such as scrambler seed field 622, and/or anaddress field, such as address field 636 may be decoded for determiningwhether the second portion is present. For example, if the address field636 represents a multicast address, and one or more particular fields ofthe frame control field 632 are set to one (1), this may indicate thatthe second portion is present in some aspects.

In some aspects, an address field of the first portion may be decodedfor determining whether the second portion is present in the PPDU. Forexample, if the address field is a multicast address or a localizedaddress, method 1100 may determine the second portion is present. Insome aspects, if the address field is both multicast and localized, themethod 1100 may determine the second portion is present, but otherwisethe second portion may be determined not to be present.

If the second portion is not present, decision block 1120 takes the “No”branch, and processing continues. If the second portion is present,process 1100 moves to block 1125, where, at least non-legacy devicescapable of receiving at a second data rate do receive the second portionat the second data rate, which is higher than the first data rate. Insome aspects, the second portion may be received at the same data rateas the first portion. However, even when the first and second portionsare received at the same data rate, the conditional processing describedabove with respect to block 1115, where the first device determineswhether the second portion is still present, may still be performed.

In block 1130, the second portion is decoded for determining whetherpermission is granted for the first device to transmit as part of amulti-user uplink transmission during the non-contention period. Inother words, multiple devices may transmit during the non-contentionperiod, with each device transmitting using at least some differingtransmission parameters. Thus, any individual transmitting devicerepresents only a portion of the total multi-user transmission occurringduring the non-contention period.

In some aspects, whether permission is granted is based on whether thefirst device is identified in the second portion of the PPDU via thefirst devices's address, AID, or a group identifier associated with thefirst device (as shown and discussed above with respect to FIGS. 7-8).If the first device is not identified in the second portion, decisionblock 1135 takes the “No” branch, and processing continues. If the firstdevice is identified, block 1140 decodes the second portion fordetermining parameters for the uplink transmission during thenon-contention period. In some aspects, these parameters may include oneor more of the parameters discussed above with respect to FIGS. 7 and/or8. In some aspects, the parameters or scheduling information may includeone or more of bandwidth and/or subband assignments for one or moredevices participating in the multi-user transmission, how many spatialstreams are utilized in the multi-user transmission, the modulation andcoding scheme (MCS) used by each device participating in the multi-usertransmission, and a maximum length of the multi-user transmission. Inblock 1145, the first device performs part of a multi-user uplinktransmission during the non-contention period based on the decodedtransmission parameters.

In some aspects, once the second portion is determined to be present,and is received by method 1100 in block 1125, an error check value maybe decoded from the second portion. The error check value could be, invarious aspects, a parity bit or a cyclic redundancy check (CRC) or anyother error check value known in the art. An error detection method maythen be performed on the second portion based on the error check valueincluded in the second portion. If an error is detected, the secondportion may be ignored by method 1100 and not processed further.

In some aspects of method 1100, a separate network message is receivedby the first device indicating a transmission data rate of the secondportion. This indicated transmission data rate may be stored by thefirst device and relied on to determine a receiving and/or decoding rateof second portions received subsequent to the separate network message.

Therefore, the receiving and/or decoding of the second portion may thenbe based on the data rate indicated by the network message. In someaspects, the network message is a management frame, perhaps transmittedby an access point. In some aspects, the network message is notseparate, but instead may be just the first portion.

In some aspects, process 1100 includes receiving one or more additionalsymbols after reception of the second portion. The received additionalsymbols may contain random information in some aspects. In some aspects,the additional symbols may be received after a CRC or FCS covering thesecond portion is received. In some aspects, these additional symbolsprovide time for a phase locked loop (PLL) of a receiving device (forexample, a device performing process 1100) to settle before a multi-useruplink transmission begins. In some aspects, a multi-user uplinktransmission is then initiated (performed) short inter-frame space time(SIFS) after reception of the additional symbols completes.

In some other aspects, process 1100 includes transmitting a multi-useruplink transmission after an extended short inter-frame space (SIFS)time that is longer than the standard SIFS time. This extended SIFS timealso provides additional PLL (Phase locked Loop) settlement time for adevice performing a multi-user uplink transmission during thetransmission opportunity following the extended SIFS.

FIG. 11B is a functional block diagram of an apparatus 1150 for wirelesscommunication, in accordance with certain embodiments described herein.In some aspects, the apparatus 1150 is the device 302. Those skilled inthe art will appreciate that the apparatus 1150 may have more componentsthan the simplified block diagrams shown in FIG. 11B. FIG. 11B includesonly those components useful for describing some prominent features ofimplementations within the scope of the claims.

The apparatus 1150 includes a receive circuit 1155. The receive circuit1155 may be configured to perform one or more of the functions discussedabove with respect to blocks 1105 and/or 1125. In some aspects, thereceive circuit 1155 includes the receiver 312. The apparatus 1150 alsoincludes a decoding circuit 1160. The decoding circuit 1160 may beconfigured to perform one or more of the functions discussed above withrespect to blocks 1110, 1115, 1120, 1130, 1135, and/or 1140. In someaspects, the decoding circuit 1160 may include the processor 304. Thedevice 1150 also includes a multi-user uplink transmission circuit 1165.In some aspects, the multi-user uplink transmission circuit 1165 may beconfigured to perform one or more of the functions discussed above withrespect to block 1145. In some aspects, the multi-user uplinktransmission circuit 1165 may include the transmitter 310.

A person/one having ordinary skill in the art would understand thatinformation and signals can be represented using any of a variety ofdifferent technologies and techniques. For example, data, instructions,commands, information, signals, bits, symbols, and chips that can bereferenced throughout the above description can be represented byvoltages, currents, electromagnetic waves, magnetic fields or particles,optical fields or particles, or any combination thereof.

Various modifications to the implementations described in thisdisclosure can be readily apparent to those skilled in the art, and thegeneric principles defined herein can be applied to otherimplementations without departing from the spirit or scope of thisdisclosure. Thus, the disclosure is not intended to be limited to theimplementations shown herein, but is to be accorded the widest scopeconsistent with the claims, the principles and the novel featuresdisclosed herein. The word “exemplary” is used exclusively herein tomean “serving as an example, instance, or illustration.” Anyimplementation described herein as “exemplary” is not necessarily to beconstrued as preferred or advantageous over other implementations.

Certain features that are described in this specification in the contextof separate implementations also can be implemented in combination in asingle implementation. Conversely, various features that are describedin the context of a single implementation also can be implemented inmultiple implementations separately or in any suitable sub-combination.Moreover, although features can be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination can be directed to asub-combination or variation of a sub-combination.

The various operations of methods described above may be performed byany suitable means capable of performing the operations, such as varioushardware and/or software component(s), circuits, and/or module(s).Generally, any operations illustrated in the Figures may be performed bycorresponding functional means capable of performing the operations.

The various illustrative logical blocks, modules and circuits describedin connection with the present disclosure may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array signal (FPGA) or other programmable logic device(PLD), discrete gate or transistor logic, discrete hardware componentsor any combination thereof designed to perform the functions describedherein. A general purpose processor may be a microprocessor, but in thealternative, the processor may be any commercially available processor,controller, microcontroller or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

In one or more aspects, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over as oneor more instructions or code on a computer-readable medium.Computer-readable media includes both computer storage media andcommunication media including any medium that facilitates transfer of acomputer program from one place to another. A storage media may be anyavailable media that can be accessed by a computer. By way of example,and not limitation, such computer-readable media can comprise RAM, ROM,EEPROM, CD-ROM or other optical disk storage, magnetic disk storage orother magnetic storage devices, or any other medium that can be used tocarry or store desired program code in the form of instructions or datastructures and that can be accessed by a computer. Also, any connectionis properly termed a computer-readable medium. For example, if thesoftware is transmitted from a website, server, or other remote sourceusing a coaxial cable, fiber optic cable, twisted pair, digitalsubscriber line (DSL), or wireless technologies such as infrared, radio,and microwave, then the coaxial cable, fiber optic cable, twisted pair,DSL, or wireless technologies such as infrared, radio, and microwave areincluded in the definition of medium. Disk and disc, as used herein,includes compact disc (CD), laser disc, optical disc, digital versatiledisc (DVD), floppy disk and Blu-ray disc where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.Thus, in some aspects computer readable medium may comprisenon-transitory computer readable medium (e.g., tangible media). Inaddition, in some aspects computer readable medium may comprisetransitory computer readable medium (e.g., a signal). Combinations ofthe above should also be included within the scope of computer-readablemedia.

The methods disclosed herein comprise one or more steps or actions forachieving the described method. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isspecified, the order and/or use of specific steps and/or actions may bemodified without departing from the scope of the claims.

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein can bedownloaded and/or otherwise obtained by a user terminal and/or basestation as applicable. For example, such a device can be coupled to aserver to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via storage means (e.g., RAM, ROM, a physical storage mediumsuch as a compact disc (CD) or floppy disk, etc.), such that a userterminal and/or base station can obtain the various methods uponcoupling or providing the storage means to the device. Moreover, anyother suitable technique for providing the methods and techniquesdescribed herein to a device can be utilized.

While the foregoing is directed to aspects of the present disclosure,other and further aspects of the disclosure may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

What is claimed is:
 1. A method of transmitting a physical layerconvergence protocol data unit on a wireless medium, comprising:generating a first portion of the physical layer convergence protocoldata unit for transmission to a first set of devices and a second set ofdevices, the first portion including a frame having a signal field thatindicates a length of the physical layer convergence protocol data unitgreater than a length of the frame, the indicated length including atleast a portion of the length of the frame; generating a second portionof the physical layer convergence protocol data unit for communicationto one or more devices of the second set of devices that willcommunicate during a multi-user transmission; transmitting the firstportion at a first data rate, the first portion decodable by the firstand second sets of devices; and transmitting the second portion at asecond data rate higher than the first data rate, the second portiondecodable by the second set of devices.
 2. The method of claim 1,wherein the second portion is further generated to indicate schedulinginformation for the multi-user transmission and an identification of theone or more devices of the second set of devices that will communicateduring the multi-user transmission.
 3. The method of claim 2, whereinthe identification includes at least one of a station identifier, groupidentifier, and association identifier for each of the one or moredevices of the second set of devices.
 4. The method of claim 1, whereinthe second portion is generated to include an indication of one or moreof a modulation and coding scheme (MCS), bandwidth, sub-band, spatialstream information, and length information for the multi-usertransmission.
 5. The method of claim 1, wherein the first portion isgenerated to include a duration field including a data value greaterthan a combined length of the first and second portions.
 6. The methodof claim 1, wherein the generating of the second portion includesgenerating an indication of a length of the second portion.
 7. Anapparatus for transmitting a physical layer convergence protocol dataunit on a wireless medium, comprising: a processor configured to:generate a first portion of the physical layer convergence protocol dataunit for transmission to a first set of devices and a second set ofdevices, the first portion including a frame having a signal field thatindicates a length of the physical layer convergence protocol data unitgreater than a length of the frame, the indicated length including atleast a portion of the length of the frame, and generate a secondportion of the physical layer convergence protocol data unit forcommunication to one or more devices of the second set of devices thatwill communicate during a multi-user transmission; a transmitterconfigured to: transmit the first portion at a first data rate, thefirst portion decodable by the first and second sets of devices, andtransmit the second portion at a second data rate higher than the firstdata rate, the second portion decodable by the second set of devices. 8.The apparatus of claim 7, wherein the second portion is furthergenerated to indicate scheduling information for the multi-usertransmission and an identification of the one or more devices of thesecond set of devices that will communicate during the multi-usertransmission.
 9. The apparatus of claim 8, wherein the identificationincludes at least one of a station identifier, group identifier, andassociation identifier for each of the one or more devices of the secondset of devices.
 10. The apparatus of claim 7, wherein the second portionincludes an indication of one or more of a modulation and coding scheme(MCS), bandwidth, sub-band, spatial stream information, and lengthinformation for the multi-user transmission
 11. The apparatus of claim7, wherein the generation of the first portion includes generating aduration field storing a value greater than a combined length of thefirst and second portions.
 12. The apparatus of claim 7, wherein thegeneration of the second portion includes generating an indication of alength of the second portion.
 13. A method of receiving a physical layerconvergence protocol data unit on a wireless medium, comprising:receiving, by a wireless device, a first portion of the physical layerconvergence protocol data unit transmitted to a first set of devices anda second set of devices, the first portion including a frame having asignal field that indicates a length of the physical layer convergenceprotocol data unit greater than a length of the frame, the indicatedlength including at least a portion of the length of the frame;determining, based on the first portion, whether the physical layerconvergence protocol data unit includes a second portion transmitted ata higher data rate than the first portion; receiving the second portionat the higher data rate based on the determining; decoding the secondportion communicated to one or more devices of the second set of devicesthat will communicate during a multi-user transmission; andcommunicating during the multi-user transmission.
 14. The method ofclaim 13, wherein decoding the second portion comprises determiningscheduling information for the multi-user transmission and identifyingone or more devices of the second set of devices that will communicateduring the multi-user transmission.
 15. The method of claim 14, whereinthe identification is based on at least one of a station identifier,group identifier, and an association identifier.
 16. The method of claim13, wherein decoding the second point comprises determining one or moreparameters of the multi-user transmission including one or more of amodulation and coding scheme (MCS), bandwidth, sub-band, spatial streaminformation, and length information for the multi-user transmission. 17.The method of claim 13, further comprising: decoding the first portionfor determining a duration field having a data value greater than acombined length of the first and second portions; and setting a networkallocation vector based on the data value of the duration field.
 18. Themethod of claim 13, further comprising: decoding the first portion todetermine a length of the second portion; and decoding the secondportion based on the determined length of the second portion.
 19. Anapparatus for receiving a physical layer convergence protocol data uniton a wireless medium, comprising: a receiver configured to receive afirst portion of the physical layer convergence protocol data unittransmitted to a first set of devices and a second set of devices, thefirst portion including a frame having a signal field that indicates alength of the physical layer convergence protocol data unit greater thana length of the frame, the indicated length including at least a portionof the length of the frame; and a processor configured to determine,based on the first portion, whether the physical layer convergenceprotocol data unit includes a second portion transmitted at a higherdata rate than the first portion, the receiver being further configuredto receive the second portion at the higher data rate based on thedetermining, wherein the processor is further configured to: decode thesecond portion communicated to one or more devices of the second set ofdevices that will communicate during a multi-user transmission, andcommunicate during the multi-user transmission.
 20. The apparatus ofclaim 19, wherein the second portion is further decoded to identifyscheduling information for the multi-user transmission and anidentification of the one or more devices of the second set of devicesthat will communicate during the multi-user transmission.